Green snap (GS), also called brittle snap, refers to the stalk breakage at or below the ear node when maize is rapidly growing. GS is environmentally dependent. It is hard to predict the severity of the phenomenon. Abiotic factors that are observed to cause GS include strong winds at the most vulnerable growth stage, excessive nitrogen treatment, high temperature and high soil moisture conditions (Elmore, 1999, 2003; Wilhelm, 1999). However, GS is conditioned not only by environmental factors. The genetics of maize also has a significant contribution. It has been observed that certain lines of maize are more tolerant to GS than others.
Green snap could lead to yield loss up to 90% when high wind passes through the corn fields during the rapid growth (elongation) period of vegetative growth. It is not a rare phenomenon. In July 1993 and 1994, severe storms with wind at 100 mph wiped across the western U.S. corn belt, destroyed many corn fields. Almost every other year, green snap causes significant damages in Nebraska, Iowa, Minnesota, Illinois, and periodically in Ohio. However, GS is unpredictable. It depends on both biotic and abiotic factors. The same variety of corn planted a few days apart could have different levels of GS.
Meanwhile, the yield effects of GS may not be as straightforward as suggested by Roger Elmore and Richard B. Ferguson from the University of Nebraska-Lincoln in a linear fashion (based on data from 1993 and 1994): decrease 1% for every 1% increase in stalk breakage. Studies from the University of Minnesota indicate that the grain production of standing plants might compensate for grain loss from broken plants. Depending on where the breakage occurs, stalks broken below the dominant ear have significantly higher yield loss than above the ear with an average of an additional 16 percent less yield.
Green snap has become an increasing issue for seed industries producing high yielding hybrids. The corn hybrids tend to be tall and grow fast, which make them GS-vulnerable. Ironically, the best farming practice, rotating with soybean, tilling, efficient nitrogen use, high moisture and the use of fungicide with growth regulator make the plants more susceptible to the GS. Although genetics have been an effective way to fight against damages from GS, not many studies underlining the resistance has been published. Corn researchers at Pioneer Hi-Bred International (PHI) have modified a mechanical detasseler to snap corn stalk mimicking the natural GS damage (Barreiro et al, 2011). With its artificial breakage device, PHI has successfully selected high yield hybrids with moderate to high level of GS tolerance. In 1999, Benson presented his QTL analysis in an elite non-stiff stalk breeding population in the 63rd Corn and Sorghum Research Conference. In his study, three QTLs explained 66% of the genetic variation.